Low-frequency pressure fluctuations in axisymmetric turbulent boundary layers

Panton, Ronald L.; Goldman, A.; Lowery, R. L.; Reischman, M. M.

doi:10.1017/s0022112080002571

Cited by 42 publications

(30 citation statements)

References 16 publications

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“…In the ZPG boundary layer (figure 20a), the 'lobes' are aligned horizontally, in agreement with prior data based on wall pressure in, e.g. Panton et al (1980) and Kobashi & Ichijo (1986). A possible explanation for this trend, following Thomas & Bull (1983), involves the integral of the Poisson equation,…”

Section: Elevationsupporting

confidence: 88%

Effect of mean and fluctuating pressure gradients on boundary layer turbulence

2014

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This study focuses on the effects of mean (favourable) and large-scale fluctuating pressure gradients on boundary layer turbulence. Two-dimensional (2D) particle image velocimetry (PIV) measurements, some of which are time-resolved, have been performed upstream of and within a sink flow for two inlet Reynolds numbers, Re θ (x 1 ) = 3360 and 5285. The corresponding acceleration parameters, K, are 1.3 × 10 −6 and 0.6 × 10 −6 . The time-resolved data at Re θ (x 1 ) = 3360 enables us to calculate the instantaneous pressure distributions by integrating the planar projection of the fluid material acceleration. As expected, all the locally normalized Reynolds stresses in the favourable pressure gradient (FPG) boundary layer are lower than those in the zero pressure gradient (ZPG) domain. However, the un-scaled stresses in the FPG region increase close to the wall and decay in the outer layer, indicating slow diffusion of near-wall turbulence into the outer region. Indeed, newly generated vortical structures remain confined to the near-wall region. An approximate analysis shows that this trend is caused by higher values of the streamwise and wall-normal gradients of mean streamwise velocity, combined with a slightly weaker strength of vortices in the FPG region. In both boundary layers, adverse pressure gradient fluctuations are mostly associated with sweeps, as the fluid approaching the wall decelerates. Conversely, FPG fluctuations are more likely to accompany ejections. In the ZPG boundary layer, loss of momentum near the wall during periods of strong large-scale adverse pressure gradient fluctuations and sweeps causes a phenomenon resembling local 3D flow separation. It is followed by a growing region of ejection. The flow deceleration before separation causes elevated near-wall small-scale turbulence, while high wall-normal momentum transfer occurs in the ejection region underneath the sweeps. In the FPG boundary layer, the instantaneous near-wall large-scale pressure gradient rarely becomes positive, as the pressure gradient fluctuations are weaker than the mean FPG. As a result, the separation-like phenomenon is markedly less pronounced and the sweeps do not show elevated small-scale turbulence and momentum transfer underneath them. In both boundary layers, periods of acceleration accompanying large-scale ejections involve near-wall spanwise contraction, and a high wall-normal momentum flux at all elevations. In the ZPG boundary layer, although some of the ejections are preceded, and presumably initiated, by regions of adverse pressure gradients and sweeps upstream, others are not. Conversely, in the FPG boundary layer, there is no evidence of sweeps or adverse pressure gradients immediately upstream of ejections. Apparently, the mechanisms initiating these ejections are either different from those involving large-scale sweeps or occur far upstream of the peak in FPG fluctuations.

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Section: Elevationsupporting

confidence: 88%

Effect of mean and fluctuating pressure gradients on boundary layer turbulence

2014

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“…7,[10][11][12][13][14][15][16][17][18][19][20] Turbulent sources in the inner region (y ϩ Ͻ30) contribute to the high frequency band of the wall pressure spectrum. ͑The ϩ superscript denotes nondimensionalization of the distance from the wall y with the friction velocity u and the kinematic viscosity .͒ Through the use of conditional sampling techniques ͑see Wilczynski et al 21 for a review͒, large amplitude wall pressure fluctua-tions have been associated with the burst-sweep cycle.…”

Section: Introductionmentioning

confidence: 99%

“…The turbulent sources in the outer region of the boundary layer (y/␦Ͼ0.6), including the interface between the boundary layer and the potential region outside the boundary layer, contribute to the low frequency portion of the wall pressure spectrum. 11,14,16,26 The objective of the investigation described here was to determine the spanwise relationship for the wall pressure beneath a turbulent layer on a long cylinder. This included determination of the average spanwise relationship of the wall pressure based on cross correlation, coherence and circumferential mode decomposition, as well as evaluation of the spanwise relationship of particularly energetic wall pressure events.…”

Section: Introductionmentioning

confidence: 99%

Spanwise structure of wall pressure on a cylinder in axial flow

1999

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The spanwise structure of wall pressure fluctuations was measured in an axisymmetric turbulent boundary layer on a cylinder parallel to the mean flow at a momentum thickness Reynolds number of 2530 and a boundary layer thickness to cylinder radius ratio of 4.81. The measurements were made using miniature hearing aid type condenser microphones with spanwise separations of 0°, 10°, 20°, 30°, 60°, and 90°. An improved wall pressure power spectrum was obtained at low frequencies by utilizing a two-point subtraction method to remove low frequency acoustic background noise of the wind tunnel. The spanwise correlations indicate that the spanwise coherent length of the wall pressure is 30°(78/u or 0.11␦͒. The spanwise coherence is weak and concentrated in a frequency band that is substantially lower than the most energetic frequency band of the wall pressure spectrum. A mode number-frequency decomposition of the wall pressure spectrum indicates that the greatest quantity of energy is in the circumferential modes nearest zero. Modes Ϫ4 to 4 contain most of the wall pressure energy. Conditional sampling by pressure peak and VITA detection schemes ͑where VITA was applied to wall pressure to detect strong pressure gradient events͒ indicate that the spanwise extent of the high pressure peaks and high wall pressure gradients is 60°( 156/u or 0.22␦͒.

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“…Associate Technical Editor: D. M. Bushnell. space (for example, WiUmarth, 1975) and Panton, 1980). Related quantities have been studied in physical and frequency space, S pp (£, f, co), by among others, Bull (1967), Blake (1970), WiUmarth (1970), for aerodynamic boundary layers, and by Carey (1967), Bakewell (1968), and Benarrous (1979) for hydrodynamic boundary layers.…”

Section: Introductionmentioning

confidence: 99%

The Wavenumber-Phase Velocity Representation for the Turbulent Wall-Pressure Spectrum

Panton

Robert

1994

Journal of Fluids Engineering

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Wall-pressure fluctuations can be represented by a spectrum level that is a function of flow-direction wavenumber and frequnecy, $(k u co). In the theory developed herein the frequency is replaced by a phase speed; u> = ck h At low wavenumbers the spectrum is a universal function if nondimensionalized by the friction velocity u* and the boundary layer thickness 8, while at high wavenumbers another universal function holds if nondimensionalized by u* and viscosity v. The theory predicts that at moderate wavenumbers the spectrum must be of the form $ + (k\, co + =c + k\) = k\~2P + (Ac + ) where P + (Ac + ) is a universal function. Here Ac + is the difference between the phase speed and the speed for which the maximum o/$ + occurs. Similar laws exist in outer variables. New measurements of the wall-pressure are given for a large Reynolds number range; 45,000 < Re= U 0 8/v< 113,000. The scaling laws described above were tested with the experimental results and found to be valid. An experimentally determined curve for P + (Ac + ) is given.

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Low-frequency pressure fluctuations in axisymmetric turbulent boundary layers

Cited by 42 publications

References 16 publications

Effect of mean and fluctuating pressure gradients on boundary layer turbulence

Effect of mean and fluctuating pressure gradients on boundary layer turbulence

Spanwise structure of wall pressure on a cylinder in axial flow

The Wavenumber-Phase Velocity Representation for the Turbulent Wall-Pressure Spectrum

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